The present invention relates to a highly paraffinic (at least 50% C10 to C20 paraffins) diesel fuel having a very high iso-paraffin to normal paraffin mole ratio.
U.S. Pat. No. 4,594,468 teaches that it is desirable to have a low iso/normal ratio of paraffins in gas oils made from Fischer Tropsch catalysts. The examples show normal/iso ratios of from 2.7:1 to 7.5:1 (iso/normal ratios of from 0.13:1 to 0.37:1) in conventional processes and from 9.2 to 10.5:1 (iso/normal ratios of from 0.095:1 to 0.11:1) for examples of its invention.
U.S. Pat. No. 5,135,638 discloses isomerizing a waxy feed over a catalyst comprising a molecular sieve having generally oval 1-D pores having a minor axis between 4.2 xc3x85 and 4.8 xc3x85 and a major axis between 5.4 xc3x85 and 7.0 xc3x85, with at least one group VIII metal. SAPO-11, SAPO-31, SAPO-41, ZSM-22, ZSM-23 and ZSM-35 are disclosed as examples of useful catalysts.
U.S. Pat. No. 5,689,031 teaches a clean distillate useful as a diesel fuel, produced from Fischer-Tropsch wax. The isoparaffin/normal paraffin ratio is given as being from 0.3:1 to 3.0:1, preferably from 0.7:1 to 2.0:1.
U.S. Pat. No. 5,866,748 teaches a solvent (not a diesel fuel) produced by hydroisomerization of a predominantly C8-C20 n-paraffinic feed. The isoparaffin/normal paraffin ratio is given as being from 0.5:1 to 9.0:1, preferably from 1:1 to 4:1.
Two papers, xe2x80x9cStudies on Wax Isomerization for Lubes and Fuelsxe2x80x9d Zeolites and Related Microporous Materials: State of the Art 1994 Studies in Surface Science and Catalysis, Vol. 84, Page 2319 (1994), and xe2x80x9cNew molecular sieve process for lube dewaxing by wax isomerizationxe2x80x9d Microporous Materials 2 (1994) 439-449, disclose dewaxing by a catalytic (Pt-SAPO-11) wax isomerization process. These papers disclose isomerization selectivity for n-hexadecane of from 93% to 84% at 89% to 96% conversion, respectively, for iso/normal ratios of from 7.4:1 to 20.7:1. A third paper, xe2x80x9cWax Isomerization for Improved Lube Oil Quality,xe2x80x9d Proceedings, First International Conference of Refinery Processing, AlChE Natl. Mtg, New Orleans, 1998, discloses isomerization selectivity for n-C24 lube oil of from 94% to 80% at 95% to 99.5% conversion, respectively, for iso/normal ratios of from 17.8:1 to 159:1.
The present invention provides a highly paraffinic (at least 50% C10 to C20 paraffins) diesel fuel having a very high iso-paraffin to normal paraffin mole ratio. The diesel fuel must have an iso-paraffin to normal paraffin mole ratio of at least 21:1, most preferably at least about 30:1.
In both embodiments, preferably the diesel fuel has a total paraffin content of at least 90%. The term xe2x80x9ctotal paraffin contentxe2x80x9d refers to the percentage of the diesel fuel that is any type of paraffin (iso-paraffin or normal paraffin). Preferably, the diesel fuel is derived from a Fischer-Tropsch catalytic process.
The diesel fuel can be produced by contacting a highly paraffinic feed in an isomerization reaction zone with a catalyst comprising at least one Group VIII metal and a molecular sieve having generally oval 1-D pores having a minor axis between 3.9 xc3x85 and 4.8 xc3x85 and a major axis between 5.4 xc3x85 and 7.0 xc3x85. The molecular sieve can be selected from the group consisting of SAPO-11, SAPO-31, SAPO-41, ZSM-22, ZSM-23, ZSM-35, and mixtures thereof. More preferably, it is selected from the group consisting of SAPO-11, SAPO-31, SAPO-41, and mixtures thereof. Most preferably, it is SAPO-11. Preferably, the Group VII metal is selected from the group consisting of platinum, palladium, and mixtures thereof.
Preferably, the process is carried out at a temperature of from 200xc2x0 C. to 475xc2x0 C., a pressure of from 15 psig to 3000 psig, and a liquid hourly space velocity of from 0.1 hrxe2x88x921 to 20 hrbxe2x88x921. More preferably, it is carried out at a temperature of from 250xc2x0 C. to 450xc2x0 C., a pressure of from 50 to 1000 psig, and a liquid hourly space velocity of from 0.1 hrxe2x88x921 to 5 hrxe2x88x921. Most preferably, it is carried out at a temperature of from 340xc2x0 C. to 420xc2x0 C., a pressure of from 100 psig to 600 psig, and a liquid hourly space velocity of from 0.1 hrxe2x88x921 to 1.0 hrxe2x88x921.
Preferably, the process is carried out in the presence of hydrogen. Preferably, the ratio of hydrogen to feed is from 500 to 30,000 standard cubic feet per barrel, more preferably from 1,000 to 10,000 standard cubic feet per barrel.
Preferably, the feed has at least 80% C10+ normal paraffins, more preferably at least 90% C10+ normal paraffins. Preferably, the feed is derived from a Fischer-Tropsch catalytic process.